Pharmacological Characterization of Vasomotor Responses in the Tree Shrew (Tupaia belangeri) Basilar Artery: A...

The tree shrew (Tupaia belangeri) is increasingly recognized as an important experimental model for studying human diseases due to its close phylogenetic relationship with humans. Because the basilar artery's response to endogenous vasoactive mediators varies among species, we investigated the effects of vasoactive substances on isolated tupaia basilar arteries to determine whether this species is suitable as a human model. 5-Hydroxytryptamine (5-HT) and histamine (His) induced contraction, while bradykinin (BK) and acetylcholine (ACh) produced concentration-dependent relaxation. Pharmacological analysis revealed that contractions triggered by 5-HT were regulated through 5-H₁ and 5-HT₂ receptors, while His-induced responses were mediated by H₁ receptors. BK-induced relaxation was inhibited by the B₂ antagonist HOE140 and N^ω-nitro-L-arginine (L-NA), but not by B₁ antagonists or indomethacin, suggesting a B₂ receptor-mediated nitric oxide (NO) pathway. ACh-induced relaxation was markedly reduced in the presence of L-NA and the M₃ antagonist pFHHSiD, indicating M₃ receptor-mediated NO release. At basal tone, L-NA evoked a contractile response, while indomethacin led to relaxation, suggesting basal regulation by NO and prostanoids. These findings demonstrate that 5-HT₁/5-HT₂ and H₁ receptors mediate contraction, while B₂ and M₃ receptors mediate relaxation in the tupaia basilar artery. This study highlights species-specific cerebrovascular regulation and supports the tupaia as a relevant model for investigating human cerebrovascular physiology and pathophysiology.